The present invention relates to a method of performing angiography by using calcein as the fluorescent indicator substance and also to a method of performing photocoagulation therapy and angiography.
Photography of the circulatory system of the eye and angiography of the ocular fundus require the absorption of a fluorescent indicator substance or dye into the blood as it flows through the vasculature of the eye. Investigators have reported the use of soduim fluorescein (Naf), carboxyfluorescein (CF), indocyanine green, lissamine green, patent blue, Evans blue, and acridine orange as dyes suitable for angiography. Fluorescein angiography is one of the most improtant tools in diagnosing retinal-chloroidal diseases. Sodium fluorescein and indocyanine green are the two agents currently used as indicators for angiography of the retinal and choroidal vasculature. Sodium fluorescein is the only fluorescent dye currently in clinical use.
Sodium fluorescein has its light absorption peak near 490 nm and it fluoresces maximally at 514 nm to 520 nm. The molecular weight of sodium fluorescein is 376 and it has a relatively high lipid solubility. Sodium fluorescein is readily metabolized to fluorescein glucuronide, which is weakly fluorescent and easily crosses the blood-ocular barrier. Given these factors, angiograms taken with sodium fluorescein have a relatively short decay time in the retinal vasculature. Also, with sodium fluorescein, fluorescein leakage into the vitreous tends to obscure retinal and choroidal structures in later phases which hinders or prohibits photocoagulation therapy prior to or after angiography.
Carboxyfluroescein is another fluorescent dye which has been used for fundus angiography. Carboxyfluorescein is a hydrophilic derivative of fluorescein. The light absorption peak of carboxyfluorescein is 490 nm and it fluoresces maximally at 520 nm. Carboxyfluorescein has a molecular weight of 373. The main distinction between carboxyfluorescein and sodium fluorescein is that carboxyfluorescein has 1/1000 the lipid solubility of sodium fluorescein and thus is less likely to penetrate cell membranes. Studies of carboxyfluroescein used in fluorophotometry to investigate blood-ocular barriers indicate that it may delineate certain abnormalities of these barriers better than sodium fluorescein. Because carboxyfluorescein is not as readily glucuronated as sodium fluorescein, carboxyfluorescein also has been used as a tracer in quantitative physiological studies of the anterior chamber of human eyes.
Although sodium fluorescein and carboxyfluorescein are suitable for angiography there is a need for a fluorescent dye which has a longer circulation decay time than that of these and any other known fluorescent indicator. Additionally, there is a need for a fluorescent dye which has limited leakage to permit simultaneous angiography and photocoagulation therapy without obscuring the fundus view with leaking dye from the photocoagulated structure.